Apparatus and method for illuminating and imaging the retina of an eye of a patient

ABSTRACT

An apparatus for illuminating and imaging the retina of an eye of a patient utilizes an LED as source of illumination.

RELATED APPLICATIONS

This application is a continuation of Ser. No. 11/581,020 filed Oct. 13,2006 entitled APPARATUS AND METHOD FOR ILLUMINATING AND VIEWING THEANTERIOR SEGMENT OF AN EYE OF A PATIENT which is a continuation of Ser.No. 11/158,426, filed Jun. 22, 2005, now U.S. Pat. No. 7,121,665 issuedOct. 17, 2006, which is a divisional application of Ser. No. 10/758,695,filed Jan. 15, 2004, now U.S. Pat. No. 6,921,169 issued Jul. 26, 2005,which is a continuation application of Ser. No. 10/033,432 filed Dec.26, 2001, now U.S. Pat. No. 6,685,317 issued Feb. 3, 2004, which is acontinuation application of Ser. No. 09/592,899 filed Jun. 13, 2000, nowU.S. Pat. No. 6,361,167 issued Mar. 26, 2002. All applications arehereby incorporated by reference for all purposes.

FIELD OF THE INVENTION

This invention relates to eye cameras and in particular to digital eyecameras.

BACKGROUND OF THE INVENTION Eye Examinations

Eye health-care practitioners generally divide patient examination intothree parts: examination of the cornea, examination of the retina, and avision function exam including measurement of the refractive status ofthe eye. The doctor's findings need to be recorded and the standardmethod for last century has been to make hand-written notes in thechart. Hand recording of vision function and refractive status iscompletely satisfactory. Vision function is basically a quantitativeassessment by the doctor and six numbers describe the refractiveinformation of both eyes so that the manual recording process is quickand efficient. Recording the clinical status of the cornea and retina iscompletely different.

For the retinal and corneal eye-health exams what is needed isquantitative clinical data but what has usually been recorded in thepast is the doctor's clinical assessment. For example, an examiner mayrecord, “the optical disk has a normal pallor” which is the clinicalperception or, even more simply, the diagnoses, “this patient does nothave glaucoma”. Seldom is the actual clinical information recorded,which, in this instance, would be a color image of the optical disk.This lack of documentation leaves open an opportunity for latercriticism that the examination or diagnoses was faulty. Further, it iswell known in the instance of estimating the pallor, the cup-to-diskratio, and the like, that making assessments of these quantities aredifficult and that the intra-observer variation is large. Especially forthese examples, it would be quite beneficial to have a method for makinga detailed comparison of changes in the optical disk between exams.

Most retinal exams are accomplished by using the optical aids of thedirect ophthalmoscope, binocular indirect ophthalmoscope (BIO) or aspecial lens with the slit-lamp/biomicroscope.

Direct Ophthalmoscope

The direct ophthalmoscope consists of a light and single lens heldbetween the doctor's and patient's eye by which the doctor can visualizea very small segment of the retina at a time. The light is considereduncomfortably bright by most patients and skill is required on the partof the clinician. By scanning the visualized area about, a mental imageof the posterior pole may be obtained for a basic assessment of retinalhealth. It is difficult to simply stop the scan and study a given areasuch as the optical disk because of patient motion and discomfort.

Binocular Indirect Ophthalmoscope

For a more complete visualization of the retina, a BIO may be used. TheBIO comprises a lens mounted on a headband in front of each of thedoctor's eyes, a single lens held by hand close to the patient's eye,and a light also mounted on the doctor's headband. The field-of-viewvisualized is wider than that of the direct ophthalmoscope and thisinstrument is generally used through dilated pupils. With the BIO thedoctor can more thoroughly examine the periphery of the retina. Usingthe BIO requires a great deal of clinical skill and is usually learnedover a period of an entire year while the doctor is in training.However, like the direct ophthalmoscope, the doctor must develop amental picture of the broader features of the eye and, because of thebright light and movements of the patient's eye, it is difficult to stopand carefully study one portion of the retina.

Slit-Lamp Biomicroscope

The slit-lamp is designed for corneal visualization. This instrument isa binocular microscope and a small lamp that projects a narrow rectangleof light into the anterior structures. This microscope, with a speciallens and the slit-lamp light, can be used for retinal visualization aswell. However, when modified for retinal imaging, its inherentlimitations generally prevent it from providing high quality retinalvisualizations. The examination can only be done on patients with adilated iris. The lens is positioned to be very close to the patient'seye, which in turn makes it very difficult to determine and adjust thealignment for the lens. The contact type lens can be very uncomfortableto the patients. The lens produces strong light reflection from itssurfaces, which deteriorate the quality of retinal image greatly.However, with only a slit of light, only small portions of the retinacan be observed at a time and patients generally feel that the lightintensity if very uncomfortable. Overall, modifications on the slit lampbiomicroscope produce a very substandard retinal visualization system.

Dilation and Bright Lights

Currently, for a through eye exam, and almost always when the BIO isused, it is necessary to dilate the patient's eye. Dilation comprisesthe application of eye drops that open the iris to a larger than normaldiameter and can not be applied until the refraction portion of the examis completed. Significant time is required for the drops to take effect.During this time the patient is almost always taking up limited space inthe examination room. Further, dilation is very objectionable topatients because of the elapsed time for the dilation to return tonormal. Studies show that this alone is a major factor for patients todefer having eye exams. Most patients also find the brightness of thelight objectionable and many times to the point of pain. While someBIO's come equipped with head-mounted cameras, these have not beenwidely accepted, are regarded as difficult to use, and only image asmall portion of the retina at a time in any instance. A hazard ofdilation is the risk of inducing acute glaucoma that can lead toimmediate blindness. Thus, a system that can accomplish an exam withlittle or no dilating eye drops and no bright light would be of greatadvantage.

Prior Art Eye Cameras

Fundus Cameras

For accurate documentation sometimes fundus cameras are used as asupplement or replacement for the manual retinal exam. These camerashave been in use since the 1940's and most of them record images of theretina on film. Film has the disadvantage of requiring processing beforean assessment of image quality can be obtained and there is no abilityto immediately electronically transfer the image. Some cameras are nowbeing equipped with digital imaging add-on capability. By digitalimaging we mean the use of an electronic image sensor such as CCD orCMOS followed by digitization and digital storage means.

In current practice these digital add-ons to existing cameras and arequite bulky and expensive. As a consequence, fundus cameras, digital orfilm, are usually located in a separate room and a specializedtechnician is employed to operate them. The high level of acquisitionand operating costs for digital cameras has left digital imaging to thedomain of high-end clinical sites and they are not used for routineexams. Digital cameras have also been added to slit-lamp biomicroscopesso that they can be used for imaging, but this single purposeapplication has generally proved to not be cost effective and is seldomimplemented.

Use of Fundus Cameras for Cornea Viewing

Although designed for retina imaging, the fundus camera has been used toimage the cornea. However, the camera generally produces low qualitypictures because the inherent achromatic and spherical opticalaberrations when used with an air path and are high and the camera hasonly a very limit working range. When the cornea is in focus, thepatient's eye is located so close to the camera that it becomesdifficult to place a slit-lamp between them and no known commercialproduct provides a slit-lamp with the fundus camera. If a slit-lamp wereadded, the lamp would block or distort the view of camera when it ispositioned in the front of the objective lens. The built-in internalmagnification adjustment for the fundus camera is not adequatelydesigned for the required magnifications of corneal imaging. Thus, as apractical matter, using the fundus camera for corneal imaging is verynon-optimal.

Scanning Laser Ophthalmoscope

In yet another prior art retinal imaging approach, a mechanically drivenmirror is used to scan a laser beam about the retina and the reflectedintensity is measured to generate an image. These imaging systems,commonly called a scanning laser ophthalmoscope or SLO, usually onlyprovide one laser wavelength and this therefore does not produce a colorimage, a significant clinical disadvantage. Recently, a system wasprovided to the market with two laser colors, but even this producesvery, very poor color image quality. Even greater limitations are in therelatively long exposure time that allows eye movement during the frametime, the large size, and the high cost.

Prior Art Laser Eye Surgery

The laser has been widely used in treatment of various diseases in theanterior and posterior segment of the eye. The BIO or biomicroscope isone method used to deliver the laser to retinal or corneal region. Toalign the clinician's eye, the condensing lens and patient's eye must bein line for viewing, and at same time the laser spot must be directed tothe intended area. This is a very challenging task. The slit-lampbiomicroscope, with additional laser delivery attachment and a laserlens (contact or noncontact), is the most commonly used platform.Although it provides a more stable condition for laser procedure, theexternal attachment makes the system complicated to use. The laser lensis very often being held by one hand of the clinician. Any motion of thelens causes the viewed retinal image to move, especially in the case ofhigh magnification lens. It is not comfortable to hold the laser lenssteady during the long laser treatment session which can last forseveral minutes. The regular illumination to the retina is provided bythe slit-lamp lamp in this case. To avoid blocking the laser beam theclinician must maintain certain positions with the slit-lamp whilesimultaneously projecting the light to the desired area. In addition,the reflected laser light from the laser lens can scatter back in manydirections in the room, a result hazardous to others present. Viewingthrough the biomicroscope and laser lens, the clinician can notsimultaneously see the iris and make the judgment on the state ofalignment for the lens. As result, there is the risk of accidentallyfiring the laser on to the iris. The nature of the manual manipulationof the laser beam also makes it difficult to assess the dosage of laserbeing delivered to the retina if no clear marks are left after thetreatment. In a new treatment, photodynamic therapy, the laser powerlevel is below that which would leave a mark on the retina. This, thecontrol of the laser dosage is very critical in PDT treatment.Sometimes, a completely separate system is provided for laser treatment,adding to the expense to well equip an eye doctors office.

What is needed is a relatively low cost, digital, and eye camera formonitoring and recording the conditions of the retinal and cornealregions of the eye. This system would have even greater value if itcould be additionally used for laser treatment and retinal stimulus forvisual function testing.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a drawing of a preferred embodiment of the invention.

FIG. 2 is a drawing showing the optical layout of the retinal imagingportion of the preferred embodiment.

FIG. 2A is a drawing showing the grouping of the elements of FIG. 2 intoan objective module, a relay module, and an imaging module.

FIG. 3 is a drawing of a preferred ring light source.

FIGS. 4, 4A, and 5 are drawings showing the corneal imaging portion ofthe preferred embodiment.

DETAILED DESCRIPTION OF THE INVENTION First Preferred EmbodimentExternal Design

In FIG. 1 is shown the exterior design of a first preferred embodimentof the present invention. A typical headrest 1 and chin rest 2 isprovided to stabilize the patient head.

The slit lamp 3 provides illumination for examination of the cornea andis adjustable in brightness, color, and width of slit.

The base 4 provides the usual degrees of freedom in angular, transverseand longitudinal motion. Inside of the camera are means for adjustingthe height of the camera potentially through a motorized system.Joystick 5 assists in controlling motion and has control switches foroperation of the system. In FIG. 1, the joystick 5 is shown on base 4.Alternatively, the joystick 5 can be mounted on a portable base, and beplaced on different position away from the base 4.

A small LCD display 6 can be used to display the image, especially areal-time infrared corneal image. However, the main image display is alarger monitor and is not shown. Oculars 7 are provided for achievingall of the typical visual functions associated with the slit-lampbiomicroscope. Lens 12 is the front objective lens and seals the opticalsystem. Various controls 8 for magnification, light level and the likeare located on the side of the camera. The dimensions of the camera aresimilar to those of the conventional slit-lamp biomicroscope.

Retinal Imaging

Referring to FIG. 2, the retina 9 is the back portion of the eye and isa curved object plane. The vitreous 11 is a non-achromatic gel thatfills the eye. Thus one challenge of the optical system will be to imagethe curved plane of the retina through the non-achromatic gel onto theflat plane of the electronic area image sensor, typically CCD or CMOS,and produce high resolution achromatic images though an optical systemwhich compensates for the non-achromaticity of the eye.

The objective lens is comprised of lens elements 12 and 13. The frontlens 12 is not changed between the retinal and corneal imaging and sealsthe optical system. The second objective element 13 is internallychangeable and provides for the optical system objective lens changesnecessary for switching between the corneal and retinal imagingfunctions. This also places the lens changing mechanism inside thecamera and out of contact with the operator's fingers for safety. Therear objective lens 13 when combined with the front objective lens 12comprises the objective lens set for retinal imaging. Plane 14 is thelocation of the first real image and may contain a mask to limit thefield of view.

Mirror 15 is switched into place for the retinal-imaging task, and whenin place, blocks the view of the visualization section of the slitlamp/biomicroscope comprised of elements 35 through 37 and 7. With theminor in place the light is directed downwards and is further reflectedby minors 16 and 17 and directed to image sensor 18. Located at 19 is anaperture that is the optical aperture for the imaging system. Thisaperture is relayed to the lens of the eye to form the entrance pupil ofthe camera when in the retinal imaging mode. Lens 20 projects the imageat 14 approximately at infinity and lens 21 is movable along the opticalaxis to focus the image exactly at infinity. Lens set 22 can be insertedor removed to change the magnification of the system.

Finally, lens 23 refocuses the image onto the image sensor 18. Bychanging lens 23 sensors of various size or format can be utilized bychanging only one lens. This is a significant advantage as the sensorfor color imaging may have a different size than one optimized forangiography, which might be a larger format sensor operating in a singlecolor. It also allows the system to be retrofitted for new sensors asthey may become available.

Beam splitters 24 and 25 partially reflect light from retina 9 onto aphoto sensor 26 for auto exposure control. The beam splitter 24 alsoreflects light from light source 27 into the optical system in suchfashion that source 27 is optically conjugate to the retina 9. Thesource 27 may provide lighting for an internal fixation light and/or anauto focusing mechanism. Or, for example, it could be a programmable LCDso that a varying fixation point could be provided or sources fortesting vision could be utilized.

Masks or programmable light sources such as LCD's can be used at 27 toprovide for vision function testing. Tests such as perimetry, colorsensitivity, contrast sensitivity testing, and the like may be readilyprovided.

Source 28 provides illumination for retinal imaging and can be pulsed orcontinues. The source 28 is shaped as a ring of light and the light isinjected co-axially by lenses 29 and 30 such that a ring of light isprojected onto the eye lens of the patient but outside of the entrancepupil. The illumination light passes through the space outside themirror 17. By this fashion high contrast images can be obtained. Inplane 31, a small diameter disk shaped optical linear polarizer isplaced on the optical axis to polarize, in the plane of the paper, theportion of the illuminating beam that is on axis. There is an unwantedreflection from objective lens 12 and 13 and this reflection will bepolarized. The refection from the retina is however depolarizing. Thisunwanted reflection will only come from the center of the lens becausethis is the part of the lens where the surface is normal to the outgoingillumination beam. To block the reflection of light from the lens 12 and13 from entering the electronic camera, polarizing beam splitter 24reflects the s-polarized light and transmits the p-polarized light. Thepolarization direction of the linear polarizer at plane 31 is orientedto be normal to that of p-polarization at beam splitter (24).

To accurately align the optical system to the iris on patient's eye, aninfrared imaging system consisting of beam sampler 32, lens 33, andinfrared camera 34 is inserted into the optical path. The beam sampler32 is highly transmissive to the visual light and slightly reflectivefor infrared light. When the cornea portion of the eye is illuminated byan infrared source (not shown in FIG. 2) mounted outside the peripheryof lens 12, infrared light is collected by lens 12 and 13, and thensampled by beam sampler 32. Lens 33 forms a corneal image on the camera34. The image formed on camera 34 can be used to determine thetransverse and longitudinal alignment to the eye.

As shown in FIG. 3, a light emitting diode (LED) module 42 consists ofmultiple white color LEDs could be used to provide light for the source28. Alternatively other light sources such as flashed Xenon and Halogencould be used. The light is coupled into the entrance of fiber opticalcable 39 by a lens 40 after passing through an optical filter 41 toproperly adjust the color temperature of the light. The entrance of thefiber optical cable 39 has a shape similar to that of LED matrix onmodule 42. The exit of the fiber optical cable 39 forms a ring, whichbecomes the light source 28. The LED module 42 can work in either pulsedor continuous mode. When working in pulsed mode, the light pulse issynchronized with the trigger signals from the CCD camera. The change inthe duration of the light pulse would adjust the brightness of theimage, which is done automatically by the automatic exposure mechanism.Further compensation for the lighting condition can be adjusted manuallyif needed. If the light pulses are triggered consecutively by theimager, then a continuous illumination is perceived by the clinicianssince the frequency of the pulses is higher than human eye candistinguish. When the interlaced CCD imager is used, the pulsed mode ofillumination helps capture a single retinal picture to the computer withhigh speed and non-interlacing effect. Triggering a single light pulsesynchronized with one of two fields for the captured image frame, andremoving the light pulses before and immediately after that light pulse,will provide a full-frame image without the interlacing effect.

When working in the pulsed mode, the light pole is synchronized with thetrigger signals from the CCD camera. The change in the duration of thelight pulse would adjust the brightness of the image.

The LED module 42 can be moved out and replaced with the one consistingof multiple high power infrared or blue LEDs. These modules preferablyprovide light source for the FA and ICG sessions, and work in bothcontinuous and pulsed mode similar to that of white color LED module. Ablocking optical filter is inserted into the imaging path to block theexcitation light.

The electronically controlled actuators behind the mirror 15 can tiltthe mirror slightly along a axis within the paper plane, which in effectlaterally moves the position of the optical aperture 19 and opticalcomponents from 20 to 23 and imager 18. A trigger signal from theelectronic image sensor flashes the light source 28 and the computerrecords a digital image. As the mirror 15 is tilted to the oppositedirection, a second image is taken. When the two images are displayedseparately to left and right eyes of the clinician, a stereoscopic viewof retina is created. The amount of tilt may be introduced to the mirror16 in opposite direction to generate a more precise stereoscopic view.

Additional optical components enable the features of laser treatment.Laser 43A is guided to port 43 by an optical fiber 43B and passesthrough one of the pinholes on the pinhole array 44 that has pinholes ofvarious sizes. Additional optics may be introduced between the port 43and pinhole array 44 to homogenize the laser intensity. Lens 45collimates the laser beam to lens 47, which in turn focuses the laser tothe plane 14 and subsequently to the retina 9. The location of mirror 46is conjugate to the entrance pupil of the optical system that is locatedat the eye lens of the patient. Mirror 46 may be rotated in twoorthogonal axes in order to steer the laser beam across the retina. Withthe steering mirror located at a plane conjugate to the entrance pupilone can be assured that the laser light will inter the eye in a mannerthat the iris is not irradiated. A narrow band optical beam splitter(50) is inserted into the optical system to inject the laser light intothe optical system while allowing the visual light passing though to theimage sensor from the retina. The beam splitter 50 could also be a broadband polarization beam splitter, which reflects the s-polarized lightonly. The optical beam splitter 47 samples a small amount of laser lightonto photo sensor 48 to determine the power of the laser light. Withhelp of the image sensor the irradiance of the laser on retina can bedetermined.

In FIG. 2 the beam splitter 50 is located between mirror 17 and aperture19. However, the beam splitter 50 can actually placed anywhere along theoptical axis between the mirror 17 and image plane 14. The beam splitter50 may be located between lens 30 and mirror 17 or between light source28 and lens 29. The optical component 43 through 49 may functionsimilarly in these alternative options.

In another variation, the laser may also be projected into the opticalsystem from the space between light source 28, which is shaped as aring, and mirror 17, which may be a dichroic beam splitter. In thisinstance the laser beam is injected in the middle of the illuminationbeam. Beam splitter 50 would be eliminated, but the optical componentsin the projection system from 44 through 49 would be kept.

During the process of laser therapy, the image sensor 18 or otherdetectors may detect the motion of the retina. The retinal image and thelaser spot then can be stabilized by a servo system with twoelectrically activated actuators controlling the tilt of the mirror 16and/or 17. Also, the laser spot may track the retinal image bycontrolling the tilt of mirror 46. Also, during the laser treatment theimaging system can be operated simultaneously. Thus, angiography can beperformed simultaneous with treatment.

With a real-time image being displayed it would be possible for theclinician to mark on the displayed image the locus of the regions forintended treatment. The computer could then control the actualapplication of laser treatment with or without a manual or automatictracking system.

Corneal Imaging

To describe this embodiment utilized for the corneal imaging referenceis made to FIGS. 4 and 5. In FIG. 5 is shown a horizontal crosssectional view of the corneal imaging system in a plane on the opticalaxis line that includes the cornea 10. In FIG. 4 is shown a verticalcross sectional view of the corneal imaging system alone and through themiddle of the system and in a plane which includes the cornea 10. Inthese figures the optics which are used for retinal imaging only havebeen moved out and replaced with those used for imaging andvisualization of the anterior segment. The elements, which are changedbetween corneal and retinal imaging, include replacing mirror 15 withmirror 15A, adding elements 53, 55, 56, and 52, and replacing lens 13with lens 51.

Optical lens 12 and 51 comprise the front and rear elements of theobjective lens. Lens 12 is sealed in place and lens 13 used for retinalimaging is moved out and replaced with lens 51. Lens 12 and 51 togetherform the objective lens for the corneal imaging optical system andprovide a virtual image of the cornea at image plane 57.

When imaging or visualizing the cornea is conducted, the objective lensset projects the object to infinity. The illumination of the cornea willbe provided by the common means of a slit-lamp. Various lens sets 52 areinserted through an internal mechanism into the optical system and canbe changed for higher or lower magnification as required. The individualaxes of lenses in lens sets 52 are offset horizontally to the objectivelens set to produce a stereo image. The lens sets 52 are afocal and canbe reversed in direction to produce two magnifications for each lensset. The objective lens set redirects the individual optical axis oflens set 51 to converge at the center of the eye. By this means thecorneal imaging system provides the proper look angle for stereoscopicvision.

Following lens set 52 is a mirror 15 that can be moved into the beam todirect the rays exiting the objective lens and magnification adjustmentdownwards to the digital imaging system located vertically below orremoved to allow visualization of the cornea. The reflective coating onthis mirror is designed to be highly reflective to laser light, butpartially transmissive to the light of other wavelengths. In fact, thismirror can be a partial reflector to provide simultaneous visualobservation with digital imaging and imaging simultaneous with lasertreatment if desired.

For the visualization system, common erection prisms 36 follows imagerelay lens 35, as shown in FIG. 5. An inverted real image is formed atlocation 37. Lens sets 7 are common oculars or eyepieces and an erectimage is formed at the retina of the user's eyes 38. The optical axes ofthe two ocular paths are shown to be in parallel in FIG. 5. However, theaxes can be tilted to converge.

By changing lens set 52 a variety of magnifications are readily achievedand the eyepiece lens 7 can be exchanged as well for a wide range ofmagnifications.

When the corneal imaging system is to be used for digital imaging atleast some of the light is reflected downwards by mirror 15. The lightrays are relayed by lens 53 and 56 to form a virtual image of the corneaat plane 57. This is the same location for the image as produced by theretinal imaging system. This virtual image then can be projected to theimage sensor 18 by the lens 20, 21 and 23. Lens 20 projects the image toinfinity and lens 21 will make small adjustments to this and thereforeaccomplishes focusing. Lens 23 focuses the light onto the electroniccamera 18.

Lens 53 and 56 are aligned to the optical axis of a single lens set 52that is offset from the axis of lens 12 and 51 and image sensor 18.Prism set 55 is then used to translate the axis of the light beam fromthe offset axis to the centrally located axis of the CCD imaging system.The relay lens 53 and 56 not only form a real corneal image at plane 54,but also an entrance pupil of the imaging system at the front of lensset 52. This entrance pupil coincides with the one formed in thevisualization system.

By moving the lens 53 to be aligned to the optical axis of anothersingle lens set 52, and rotating the module consists of lens 56 andprism set 55 by 180.degree., the image from the other viewing channelcan be recorded. When the two images are displayed separately to leftand right eyes of the clinician, a stereoscopic view of anterior segmentof eye is created. The stereoscopic effect is identical to that seen bynaked eye from the binocular directly. Another stereoscopic approachwould be to align the relay lens 53 and 56 to the centrally located axisof the CCD image system and eliminate the prism set 55. Electronicallycontrolled actuators behind the mirror 15 could then tilt the mirrorslightly along an axis within the paper plane which in effect moves theimage position laterally and the optical aperture 19 and electronicimaging system behind it. Two images, taken from two oppositely tiltedminor positions, are recorded to and displayed by the computer to createthe stereoscopic effect. Compared with the directly binocularvisualization, the second approach introduces a tilt between the twoviewing channels in the digital recording. As the result, thestereoscopic effect may be slightly different from that of the firstapproach. A third approach would tilt the mirror 16 in oppositedirection from the tilt of mirror 15 to cancel out the unwanted effect.The result stereoscopic effect would be similar to that of the firstapproach.

A laser projection system identical with that used for the retinal lasersystem is formed by optical components 43 through 49 and projects laserto the cornea. The laser spot may either monitored from the image sensoralone or from both CCD camera and binoculars.

A slit lamp or other well-known means provides illumination of the eye.An LED module consists of multiple white LEDs can be used as the lightsource for the slit lamp. The light source works in either continuous orpulsed mode. When it works in pulsed mode, the light pulse issynchronized with the trigger signals from the CCD imager. A continuousillumination is then perceived by the clinicians since the frequency ofthe pulses is higher than human eye can distinguish. The brightness ofthe corneal image, observed either through the binocular or the CCDimager, is adjustable by changing the duration of the light pulse. Whenthe interlaced CCD imager is used, the pulsed mode of illumination helpscapturing a single corneal picture to the computer with high speed andnon-interlacing effect. Triggering a single light pulse synchronizedwith one of two fields for the captured image frame, and removing thelight pulses before and immediately after that light pulse does it.

Two Very Different Optical Configurations

The cornea is a slightly positively curved plane and the image path isair. The retina is a highly negatively curved plane and part of theoptical path is the vitreous. This fluid is non-achromatic so the cameramust compensate for the non-achromaticity of the media for the retinabut not so for the air path for the cornea. The present inventionachieves both of these functions, and at the high resolution requiredfor ophthalmology as well as providing multiple magnifications.

Alignment with IR Camera

The system is designed to image the retina with low dilation. To achievethis, the first design criteria is to inject the light into the eyethrough a small ring about the entrance pupil and aligning this to theiris opening. Achieving this provides uniform illumination to the retinaand a high contrast image. But, transverse and longitudinal alignmentsare critical. The use of an infrared camera operating at wavelengthsthat the eye cannot see is crucial. The infrared illumination does notcause the pupil to constrict. The IR camera is always on and focused onthe cornea even while the retinal image is being obtained and a separatedisplay shows this image. By this means the transverse and longitudinalalignment of the camera is always assured.

Entrance Pupil

Of further great challenge for the optical system is the requirement tohave different camera entrance pupil locations for the corneal andretinal imaging functions. For imaging the retina, it is of significantadvantage to place the entrance pupil of the camera at the eye lens.This reduces the effect of the aberrations of the eye and improves imagecontrast. However, for imaging the cornea, the entrance pupil must lieat the objective lens of the imaging system. The system thus operates asa “microscope” when imaging the cornea and as a “telescope” when imagingthe retina.

Projecting Images onto the Retina

Of further functional advantage is that the system provides a plane inthe instrument that is conjugate to the retina and this plane lies onthe surface of the electronic image sensor. With certain optical beamsplitters, this plane can be made accessible within the instrument atother locations for other uses. It is recognized that light emergingfrom the retina will return to and be in focus on this conjugate planeand this is the modality for imaging. However, light exiting from aplane conjugate to the retina and directed towards the eye will beprojected onto the retina. Thus, we have within the system the abilityto project light patterns onto the retina. The system could be used fortesting the performance of the eye as an imaging system. A simpleexample of this would be to project visual acuity charts or colorperception information. A more complex application would be to performperimetric measurements. In fact, a programmable LCD could be used tomodify the stimulus.

LED Module

White color LED modules consist of multiple LEDs will be used as thelight sources in both retinal imaging and corneal imaging part of thesystem. The LED module works either continuously or in pulsed mode. Itwill replace the CW light source (often halogen lamp) and flash source(often Xenon lamp) with one single source. It consumes less power,generates less heat, use less housing space, and last much longer. LEDmodules with different wavelengths will be used as light source for FAand ICG angiograms.

Stereoscopic Images

The stereoscopic images of optic nerve head have shown great clinicvalues in assessing the progress of diseases like glaucoma. The proposedsystem can take two digital images of optic nerve head from twodifferent entrance pupil positions automatically in less than 1/10 ofsecond. When the two images are displayed separately into left and righteyes, the clinician then sees and perceives the stereoscopic views ofthe optic nerve head. The stereoscopic corneal images can also be takenand displayed digitally. The proposed system can also take two digitalimages of anterior segment of the eye automatically in very short time,display stereoscopic view digitally.

Laser Treatment

One of the major treatment modalities in eye health-care is to applylaser energy to destroy portions of the retina or iris, and, with thenew photodynamic therapies, stimulate a pharmaceutical to cause thecurative effect. The proposed system provides an internally integratedlaser projection system. The laser light can be projected internallyfrom a plane conjugate to the imaging plane. No external optics orattachment is needed. The hand of clinician is free from holding thelaser lens. There will be no more scattering of laser light fromexternal optics. With the help of the infrared alignment system, thealignment is easy and simple. When the system is switched to the retinalimaging mode, the laser beam with the appropriate beam characteristicwould reach the retina. The illumination to the retina is providedinternally and independent of the positions of laser beam. Free from theglazing light reflection from the optics and cornea, the retinal imageis much clearer. When the system is switched to the corneal imagingmode, the laser would be delivered to the corneal region. In fact, withthe imaging system functioning in a real-time mode, the operator canobserve the retinal/corneal image with aiming laser spot on them, thendesignate (on the image as presented by the computer) the areas to betreated. The system, under computer control, could apply the lasertreatment. In the instance of some laser treatments, over 1,000 spotsare applied. Performing this manually is very slow but performing itunder computer control could be accomplished quickly and accurately.Further, tracking systems could be used to further stabilize the imageand/or the laser beam location. The location and accumulated energydelivery as a function of location can be determined and monitored,which is important parameter in some therapies.

Other Advantages

Because the system alignment, retinal/corneal image and aiming laserspot can be monitored and manipulated in real time remotely, theclinician is free from the restricted posture during the treatmentsession, which is the case in the current slit-lamp delivery system. Itwould greatly reduce the stress imposed on the patients and clinicians.

Further, this system can perform the popular flourescein and indocyaninegreen angiographies. Even the stereo angiograms can be recorded anddisplayed digitally. In fact, as discussed below, the system is equippedto utilize the differing format sensors that may be preferred for coloror monochrome imaging. The angiographic images can be displayed withknown scales to help determining the position and size of lasertreatment areas. During the treatment, the angiographic images can bedisplayed side-by-side with the live images of same scale on onecomputer monitor. It will greatly reduce the time and preparation workbefore a laser treatment. Laser treatments can be accomplishedsimultaneously with angiography. This gives the clinician the ability toidentify the area for treatment and monitor in real time the effect ofthe laser treatment.

As noted, digital imaging obviously eliminates the delay and cost offilm processing and assessment of image quality is immediatelyavailable. As an example of the value of examining images vs. directvisualization, studies have shown that in screening for diabeticretinopathy, a better result is obtained by examining images rather thanthe direct visualization. However, digital imaging brings othersubstantial advantages. One of the most prominent is the ability toshare findings with colleges and the like by digital transference means.That is, the actual clinical data may be obtained at one location andsent to another by electronic means for remote assessment. If one couldexamine the entire eye by digital means, a clinical assistant at aremote site could obtain the “digital copy” of the eye and transfer itto the appropriate clinical expert for review. Such a system wouldclearly need to image both the posterior and anterior segments of theeye and with high quality images.

With this system there is no need to perform an ophthalmoscopic examunless the far peripheral of the eye is to be examined. This is notroutinely done in most eye exams and is only relevant for populationswith substantially increased risk factors. However, documenting theposterior pole would be of great value for all patients. Accordingly,the time for an examination would be reduced.

While the present invention has been described in terms of preferredembodiments, the reader should understand that the invention is notlimited to those preferred embodiments. Therefore the invention is to bedetermined by the appended claims and their legal equivalents.

What is claimed is:
 1. An apparatus for illuminating and imaging theretina of an eye of a patient comprising: a light source, having an LEDas a source of illumination, configured to output a ring of illuminationlight; an objective lens module configured to direct the ring ofillumination light through the objective lens module onto the retina ofan eye of a patient and to direct light returned from retina of an eyeof a patient through the objective lens module; an electronic sensor; arelay module configured to relay the ring of illumination light from thelight source to the objective lens module and to relay light returnedfrom the retina of an eye of a patient through the objective lens moduleto the electronic sensor; and an electronic display coupled to theelectronic sensor and configured to display an image of an eye of apatient captured by the electronic sensor
 2. The apparatus forilluminating and imaging the retina of an eye of a patient of claim 1where brightness and color of the LED are adjustable.
 3. The apparatusfor illuminating and viewing the retina of an eye of a patient of claim1 where: LED brightness is adjustable by changing the duration of thelight pulse.
 4. The apparatus for illuminating and imaging the retina ofan eye of a patient of claim 1 where the electronic sensor comprises: animage sensor that receives or generates trigger pulses; and with the LEDconfigured to be pulsed in synchronism with the trigger pulses whenoperating in the pulsed mode.